The present invention relates generally to field of wireless telecommunications system design and test, and more particularly to an automated method of assigning frequencies to the sectors of a TDMA or AMPS wireless system for use during wireless system drive testing.
One of the tests commonly performed in connection with wireless telecommunications systems is the drive test. During a drive test, a technician or service engineer traverses the area under test with radio frequency measuring and recording equipment. The equipment measures and records the radio frequency signal strength at various locations in each sector or cell of the area under test. The measurements collected during the test are subjected to various analyses to determine characteristics such as cell boundary and coverage area, and to optimize the frequency plan for the network. The results of the drive test are used to adjust antenna configurations and signal strengths, and in the construction of an interference matrix, so as to optimize the system. Drive tests are conducted frequently in order to accommodate growth of system. Drive tests may be repeated for different parts of the network.
Voice channel and control channel frequencies are scarce resources. Under normal operating conditions, several voice channel frequencies are assigned to each cell or sector, and voice channel and control channel frequencies are reused throughout the system. However, during a drive test, it is necessary that each base station of a cell or sector transmit on a unique test frequency. If two or more base stations of the system are using the same test frequency, then the measurements taken in one cell or sector may be influenced by a signal transmitted from the base station of another cell or sector. Additionally, the immediately adjacent frequencies from other sectors or cells may interfere with the measurements taken for a particular frequency at a particular sector or cell. Accordingly, during a drive test, a unique test frequency must be keyed up for each sector, and that frequency and its immediately adjacent frequencies must be keyed down in each of the other sectors of the system.
Currently, cellular operators have to expend two to three weeks of engineering work to plan the frequency assignments for a drive test. During the two to three weeks of planning, the system operator must fix or freeze the frequency plan for the system, which causes great inconvenience to the operator. The engineers do the planning manually and with much trial and error. Many iterations are necessary in order to achieve an optimal plan. In most cases, however, the result is not optimal and it contains mistakes that cause the operator to repeat the process. Additionally, the scripts that operate the mobile switching center during the drive past are written manually. The manual writing of scripts typically requires about two days of engineering timing and is prone to mistakes. Since drive tests are conducted so frequently, a substantial amount of engineering resources are devoted to drive test planning.
It is an object of the present invention to provide an automated method for making drive test frequency assignments and generating drive test switch scripts.
The present invention provides an automated method of assigning frequencies to sectors of a TDMA or AMPS wireless telecommunications system for use during a drive test. The method of the present invention calculates a usage factor for each frequency that is assigned to the system to be tested. The usage factor for a particular frequency is equal to the number of sectors of the system to be tested to which the particular frequency, or an immediately adjacent frequency, is assigned. The method selects a sector and selects the frequency assigned to the selected sector with the smallest usage factor. The method keys up the selected frequency in the selected sector and keys down that frequency and the immediately adjacent frequencies in each of the other sectors of the system to be tested. The method of the present invention continues the foregoing sequence of steps until a unique frequency has been keyed up for each sector in the system to be tested.
Preferably, the method of the present invention selects the sectors in ascending order starting from the sector with the least number of frequencies assigned to it. For example, the method sorts the sectors of the system in ascending order according to the number of frequencies assigned to said sectors and proceeds through the ordered set of sectors. If, during the process, any sector reaches a minimum number of voice channel frequencies, the method of the present invention makes the remaining frequencies assigned to that sector, and their adjacent frequencies, unavailable for keying down. If a control channel frequency of a particular sector is selected to be keyed down, the method also keys down the backup control channel for that sector.
The method of the present invention is preferably implemented by means of key up and key down scripts that are run during the test. The key up script is formed by inserting the frequency selected for a particular sector in the key up script. The key down script is formed by inserting the selected frequency and the immediately adjacent frequencies in the key down script for any other sector of the system to which any of those frequencies is assigned. The key up script identifies the frequencies to keyed up for each sector during the test. Similarly, the key down script identifies the frequencies to be keyed down for each sector during the test.
The present invention is applicable to both voice channel frequencies and control channel frequencies. The user has the option to choose voice channels as dedicated key up channels, or to use control channels as key up channels, since they are transmitting all the time. The method keys up and down the assigned control channel frequencies until there are no more assigned control channel frequencies available. The method then assigns and keys up control channel frequencies for the remaining sectors from the remaining voice channel frequencies.